System with oven control and compensation for detecting motion and/or orientation

ABSTRACT

Motion and/or orientation sensing systems can utilize gyroscopes, accelerometers, magnetometers, and other sensors for measuring motion or orientation of connected objects. Temperature changes affect the precision of the data output by the motion/orientation sensing device. A system is provided for controllably heating a device within a package to a desired temperature that varies based on the ambient temperature. The operating temperature of the device can then be known and controlled. The ambient temperature can be known through an ambient temperature sensor, for example. Given this information, a controller compensates the data output by the device to further improve the accuracy in the measurements. Like the amount of heating provided to the package, the amount of compensation is also based on the ambient temperature and/or the device temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/925,349 filed Oct. 28, 2015, now U.S. Pat. No. 10,386,385 issued Aug.20, 2019, the disclosure of which is hereby incorporated in its entiretyby reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention was made with Government support under Contract No.IIP-1431016 awarded by the National Science Foundation, and underContract No. N00014-13-C-0330 awarded by the Nava STTR. The Governmenthas certain rights to the invention.

TECHNICAL FIELD

This disclosure relates to a system for controlling a heat source thatheats a motion/orientation sensing device while compensating the outputdata from the device for increased accuracy in the data.

BACKGROUND

Microelectromechanical systems (MEMS), gyroscopes, accelerometers,inertial measurement units (IWO, magnetometers and other temperaturesensitive sensors have recently improved their speed, accuracy, size,power and cost. In many applications, such as navigation, the output ofthese sensors is required to be extremely precise. A large contributorto the precision and accuracy of the sensors is their temperaturesensitivity.

SUMMARY

According to one embodiment, a system for improving accuracy of a motionor orientation sensing device includes a package having an inner surfacewhich defines an interior, and an outer surface which communicates withan ambient environment. A heat source is disposed inside the package. Atleast one internal temperature sensor is disposed inside the package andis configured to detect a temperature inside the package. A device isdisposed inside the package. The device is configured to detect movementor orientation of the attached package or surrounding attachedstructure, at least one controller programmed to (i) receive internaltemperature signals from the at least one internal temperature sensorindicating the temperature inside the package, (ii) receive signalsindicating an ambient temperature of the ambient environment, (iii)control the heat source to achieve a desired temperature inside thepackage based on the temperature signals, (iv) receive signals from thedevice indicating detected movement or orientation, and (v) compensatethe received signals from the device by a compensation factor thatvaries based on a combination of the temperature inside the package andthe ambient temperature.

The compensated signals can then be used to more accurately output amotion and/or orientation signal that is given by the device.

The system may further include an ambient temperature sensor disposedoutside of the interior of the package and configured to signalsindicating an ambient temperature of the ambient environment.

The compensation factor may vary based on a comparison between thetemperature inside the package and the ambient temperature.

The controller may further be programmed to compensate the receivedsignal from the device according to the following relationship:S _(comp) =S−(a ₁ T _(amb) +a ₂ T _(device) +a ₃)where S_(comp) is compensated output, S is the detected movement ororientation before compensation, T_(amb) is the temperature of theambient environment, T_(device) is the temperature inside the package,and a₁, a₂ and a₃ are compensation coefficients.

The signals indicating the ambient temperature of the ambientenvironment may be signals sent from a heat source indicating amagnitude of power consumed by the heat source in achieving the desiredtemperature inside the package. The at least one controller may befurther programmed to estimate the ambient temperature based on themagnitude of power consumed by the heat source.

The at least one controller may be further programmed to control theheat source such that the desired temperature inside the packageachieves a number of multiple set temperatures, each set temperaturecorresponding to a plurality of ambient temperatures.

The device may be inertial measurement unit (IMU, consisting of threeaccelerometers and three gyroscopes), one or multiple accelerometers,one or multiple gyroscopes, one or multiple magnetometers or othertemperature sensitive devices.

The number of multiple set temperatures may increase in a steppedfashion as the ambient temperature increases.

The number of multiple set temperatures may increase continuously as theambient temperature increases.

The at least one internal temperature sensor may include a firsttemperature sensor and a second temperature sensor, wherein the at leastone controller is further programmed to determine a gradient oftemperature of the package based on received signals from the first andsecond temperature sensors, and wherein the compensation factor variesbased on the gradient of temperature. The desired temperature inside thepackage may be based on the gradient of temperature.

The at least one controller may be further programmed to retrieve thecompensation factor from a calibrated lookup table based on thetemperature inside the package.

The device may be an inertial measurement unit (IMU) configured todetect movement and output the detected movement to the controller.

The heat source may be a plurality of heat sources, such as a pluralityof heaters, that are each disposed within the package and coupled to theat least one controller. The heat sources may be individuallycontrolled.

According to another embodiment, a computerized method of compensatingan output of a sensing, device configured to detect motion ororientation is provided. An internal-temperature signal is received froma temperature sensor, indicating an internal temperature within apackage. A signal is sent to a heater to heat an interior of the packageto a variable predetermined temperature. Output signals are receivedfrom a device configured to detect motion or orientation and disposedwithin the package indicating detected movement or orientation of thedevice. A signal processor compensates the output signals received fromthe device by compensation factors that vary based on the internaltemperature. The signal processor outputs compensated output signalsbased on the compensation.

According to another embodiment, a system for improving accuracy inmotion or orientation sensing device includes a package having an innersurface which defines an interior, and an outer surface whichcommunicates with an ambient environment. A heat source is disposedinside the package. A device is disposed inside the package andconfigured to detect movement or orientation. A first temperature sensoris disposed inside the package and configured to detect a firsttemperature of a first location. A second temperature sensor spaced fromthe first temperature sensor and configured to detect a secondtemperature of a second location. At least one controller is coupled tothe device, the heat source, and the first and second temperaturesensor. The at least one controller is programmed to (i) receive thefirst temperature from the first temperature sensor, (ii) receive thesecond temperature from the second temperature sensor, (iii) based onthe first and second temperatures, control the heat source to achieve adesired temperature within the package, (i) receive signals from thedevice indicating detected movement or orientation, (v) determine atemperature gradient across at least a portion of the device based onthe first and second temperatures, and (vi) compensate the signalsreceived from the device by a compensation factor that is based on thetemperature gradient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional schematic view of an environment-resistantmicro package containing a MEMS device according to one embodiment, andFIG. 1B is a perspective cross-sectional view of the package of FIG. 1A;

FIG. 2 is a cross-sectional schematic view of a micro-package containingmotion or orientation sensing device according to one embodiment;

FIG. 3 is a schematic diagram of a computerized system for measuring,motion or orientation data from the motion or orientation sensing devicewhile controlling the temperature within the packaged device andcompensating the measured output, according to one embodiment;

FIG. 4 is a flow chart illustrating an algorithm programmed into aprocessor for compensating measured output based on temperatures,according to one embodiment;

FIGS. 5A-5C are graphical illustrations of effects of temperature on asensor, and the resulting calibrated output based on the temperature ofthe sensor;

FIGS. 6A-6D are graphical illustrations of the manipulation of dataretrieved from a sensor by utilizing a single set point (SSP) oven and acalibration factor;

FIGS. 7A-7D are graphical illustrations of the manipulation of dataretrieved from a sensor by utilizing a multiple set point (MSP) oven andcorresponding calibration factors; and

FIGS. 8A-8C are graphical illustrations of manipulation of dataretrieved from a sensor by utilizing a continuous set point (CSP) ovenand corresponding calibration factors.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the embodiments. Asthose of ordinary skill in the art will understand, various featuresillustrated and described with reference to any one of the figures canbe combined with features illustrated in one or more other figures toproduce embodiments that are not explicitly illustrated or described.The combinations of features illustrated provide representativeembodiments for typical applications. Various combinations andmodifications of the features consistent with the teachings of thisdisclosure, however, could be desired for particular applications orimplementations.

References below are made to a “controller,” a “microprocessor,” a“processor,” a “signal processor,” and a CPU. It should be understoodthat all of these terms can more broadly be referred to as a“controller.” The controller is not a generic controller, but isspecifically programmed to receive temperatures from inside and/oroutside (e.g, ambient) temperature sensors and output data of a motionand/or orientation sensing device, control a heat source, and manipulatethe output of the device based on temperatures.

This disclosure describes various embodiments of MEMS devices andenvironment-resistant module including a packaged micromachined or MEMSdevice associated therewith. The MEMS device may include sensing devicesthat are configured to sense movement, motion, and/or orientation. Suchdevices include inertial measurement units (IMUs, consisting of threeaccelerometers and three gyroscopes), one or multiple accelerometers,one or multiple gyroscopes, one or multiple magnetometers or othertemperature sensitive devices. These devices can be used in a variety ofsettings to measure movement, motion, and/or orientation of a connectedobject. These devices are referred to throughout the specification as“motion or orientation sensing devices.”

To assure and maintain accurate measurement by the motion or orientationsensing device, a heat source is disposed within the package surroundingthe device. The heat source can be controlled by an associatedcontroller or microprocessor. In addition to controlling the temperatureinside the package, the controller can also compensate the output of thedevice based on a compensation factor that is set based on thetemperatures of the inside and/or outside (ambient) temperatures. Thus,temperature control and output compensation combine together to improvethe accuracy of the motion or orientation sensing device. In oneembodiment, the heat source is a heater or oven, and in otherembodiments the heat source is a circuitry with electrical resistancethat generates heat as a by-product.

FIGS. 1A and 1B are schematic views of one embodiment of a packagesurrounding the MEMS device. In a preferred embodiment, the MEMS deviceis a motion or orientation sensing device described above for measuringmotion or orientation of an associated device. The package can include:(i) a supporting substrate such as a silicon wafer or ceramic or metalsubstrate that may incorporate signal feedthroughs; a thin platformwhich provides thermal and mechanical isolation using isolationsuspensions made from the glass; and (iii) a cap silicon wafer orcapsule for final vacuum/hermetic encapsulation if needed. In oneembodiment, the MEMS die is flipped over and attached onto a glassmicroplatform, which is, in turn, supported by isolation suspensionsover a shallow recess formed in the supporting silicon wafer substrate.Interconnect lines are formed on the glass suspension beams and transferelectrical signals between pads on the glass microplatform and verticalfeedthroughs through the bottom silicon wafer.

The attached MEMS die is oven-controlled by a heat source andtemperature sensor integrated on the microplatform. As will be explainedbelow, the heat source can be controlled and the temperature inside thepackage can be set to a desired temperature. Vibration isolation isprovided by the suspensions made of the glass.

The isolation suspensions are stiff enough to mechanically support theplatform and withstand shock/vibration, but long and flexible enough toprovide thermal and vibration isolation. Both of these requirements areachieved using glass as the support and thermal isolation material.Glass has a relatively high Young's modulus and a low thermalconductivity. A thin (100 μm) glass wafer may be used to form thesesuspensions. The thin wafer is easy to etch and pattern using abatch-level wet etching process. Shock absorption layers, ananti-radiation shield for higher thermal isolation, and a getter layerfor the high vacuum environment may also be formed inside the package.

The MEMS device is fabricated on a separate substrate, and transferredonto a microplatform that is an integral part of a second wafer orsubstrate. Multiple temperature sensors and/or heat sources may be usedon one microplatform for additional precision and accuracy whenregulating temperature or to achieve a more uniform temperaturedistribution across the entire unit. The MEMS device may also be anothermicroplatform.

An oven circuit (individual die, dies or boards) may also be includedwith the MEMS device that control the temperature of the microplatformutilizing a temperature sensor and heat source that are eitherintegrated on the platform, have direct contact with the platform, orare separated from the platform.

Packaging around the MEMS device is described below. However, it shouldbe understood that, as will be described, such packaging is optional.For example, the device can be bonded to the microplatform while not ina cavity of a package; the device may be bare and not vacuum sealed,exposing the device to some surrounding environment.

If packaging is included, the transferred device may be vacuum orhermetically sealed by a cap wafer or capsule. The electrical signalleads are defined vertically on the support substrate. The verticalfeedthroughs can be formed on the cap wafer or capsule, and lateralfeedthroughs are also possible.

The packages shown in FIGS. 1A and 1B can provide isolation from twodifferent sources: mechanical and thermal input. Mechanical isolation isprovided through two elements: isolation suspensions that damp out thelow-level and higher frequency vibration signals, and shock stops thatlimit the range of travel of the transferred device during high gshocks. Thermal isolation is also provided by these isolationsuspensions, which are designed and fabricated to have very high thermalresistance. A control method can be executed to control the temperatureusing a heat source and a temperature sensor integrated on the isolationplatform or on the MEMS dies. Since the devices are highlythermal-isolated, the power consumption for the constant temperaturecontrol is very low.

The microplatform can be fabricated from a thin glass wafer, or from athick glass wafer that is mechanically thinned, or from a thickdeposited glass layer, or from a thick glass/oxide layer that isdeposited on a semiconductor wafer using a number of differenttechniques.

FIG. 2 is a more particular embodiment of the MEMS device andsurrounding packaging. In FIG. 2, the MEMS device is a motion ororientation sensing device, such as one described above. The motion ororientation sensing device includes a temperature sensor coupleddirectly to the device or adjacent the device to measure the temperatureof the device and/or its immediate surroundings. The motion ororientation sensing device is attached to the isolation platform usingconductive/non-conductive epoxy, or in another embodiment, can besurface mounted to the platform with various attachment methods. Theplatform is supported using several tethers that have interconnect linesrunning over them to electrically connect the device to pins in apackage, such as a TO-package.

As in FIG. 1A-1B, the isolation platform is fabricated from glass. To doso, a glass wafer is patterned and etched to form the isolationplatform. The platform is complete with suspensions or tethers formechanical support, thermal isolation and vibrational isolation.

In one embodiment, the heat source is a thin-film gold heater. Multipleheat sources may be provided. A heat source may be formed under thespace between the motion or orientation sensing device and the isolationplatform. Electrical signals are carried between the devices on theplatform (e.g., the motion or orientation sensing device, thetemperature sensor, the heat source, etc.) and the metal pins of thepackage using interconnect lines. These interconnect lines can be farmedand passed through tethers. A controller (not shown, but described belowwith reference to FIG. 3) controls the heat source(s) based on thetemperature readings from the temperature sensor.

In various embodiments, one or more temperature sensors can be placed invarious locations in the package: between both the motion or orientationsensing device and the platform, on the device itself, or within thepackage but separated from the device. The use of multiple temperaturesensors within the MEMS package connected to the controller allows thecontroller to determine multiple temperatures of multiple known points.Having multiple temperature sensors at different locations about themotion or orientation sensing device enables the controller to determinea temperature gradient or differential across the device, which could berelatively large when the difference between the desired heatsource-controlled temperature and the external environmental temperatureis relatively large. For example, using multiple temperature sensors andan ambient temperature sensor, the controller can determine thetemperature of the device at multiple locations and the temperature ofthe ambient outside the package; the controller is thus able todetermine the temperature gradient across the device (or across theinterior of the package) by knowing the difference in temperatures atthe different locations due to the ambient temperature. In anyembodiment, the controller can read inputs from various temperaturesensors to determine the change in the temperature inside the packageand the temperature gradient across the device. By having multiple heatsources within the package, the controller can control each heat sourceindividually to affect the temperature gradient across the package,thereby specifically and accurately controlling different areas of theinterior of the package to improve accuracy of the device.

In various embodiments, one or more temperature sensors can be placed invarious locations to deduce the temperature gradient across the motionor orientation sensing device. With the temperature gradient determined,an accurate estimation of the true temperature of the device can beestimated. For example, in one embodiment, one temperature sensor ismounted underneath the motion or orientation sensing device and anothertemperature sensor is mounted on the device. In another embodiment, onetemperature sensor is disposed within the cavity of the package, andanother temperature sensor is disposed on an outer surface of thepackage. In yet another embodiment, one or more temperature sensors aredisposed on the platform, and another temperature sensor is attachedelsewhere within the package but spaced from the device. In theseembodiments, the controller receives multiple temperature signals fromthe various temperature sensors. Based on the location of thesetemperature sensors, the controller is able to determine the differencein temperature at various locations throughout the package, or throughthe package itself. Thus, the controller can determine the temperaturegradient through the package. Based on the determined temperaturegradient, the controller can estimate the true temperature of the deviceitself if a temperature sensor is not mounted directly on the device'smeasurement region.

FIG. 3 is a schematic of the oven-control system for the motion ororientation sensing device, according to one embodiment. The hermeticpackage of FIG. 2 is shown in FIG. 3. A heat source circuit iselectrically coupled to the heat source within the package. Thetemperature sensors on or near the device as well as the temperaturesensors on or outside the package can be electrically coupled to atemperature sensor circuit shown in FIG. 3. In case the temperaturesensor is integrated inside the device, the temperature sensor circuitmay not be necessary.

The heat source circuit is electrically coupled to a microcontroller forcontrol of the heat sources within the package. The microcontroller maybe a microprocessor and may include a proportional-integral-derivativecontroller (PID controller) being configured to run a feedback controlloop. The PID controller controls the heat source. To do so, the PIDcontroller produces an output voltage signal to the beat source circuit,and the heat source circuit converts that signal into a current thatdrives the heat source. In one embodiment, the heat source circuit hasthe following relationship between the voltage signal from themicrocontroller and the current output:I _(out) g _(m) V _(in)where I_(out) is the current output from the heat source circuit to theheat sources, g_(m) is a constant conversion gain factor, and V_(in) isthe control voltage input from the PID controller to the heat sourcecircuit.

These exemplary PID controller and heat source circuit allow the heatsource within the package to be controlled so that the temperatureinside the package set to a desired temperature. And, as will bedescribed below, the microcontroller also receives signals containingdata relating to the temperature of the ambient temperature. This allowsthe microcontroller to control the heat source based on the temperatureof inside the package as well as the ambient temperature, and, as willbe described below, allows the microcontroller to compensate output datafrom the motion or orientation sensing device based on the temperatureinside the package and ambient temperature.

The microcontroller is also coupled to the outputs of the motion ororientation sensing device itself, such that the microcontrollerreceives data indicative of the inertial motion or orientation of thepackaged device and the object the package is attached to. An ambienttemperature sensor is also coupled to the microcontroller to allow thecontroller to use the ambient temperature to compensate the output data.

Since the motion or orientation sensing device can be packaged in epoxymold compound and due to the device being mounted on the platform, therecan exist inherent temperature-induced stresses based on the differencebetween the temperature and the ambient temperature. These stresses canincrease significantly when the difference in temperature between thedevice and the ambient is large. For example, an ambient temperature of−40° C. with the oven in the package attempting to maintain atemperature of 60° Cc within the package may lead to minute (butnonetheless potentially important) inaccuracies in the data output bythe motion or orientation sensing device.

In a non-limiting embodiment, the system shown in FIG. 3 is aclosed-loop system where both temperature compensation and oven controlare utilized to reduce inaccuracies that may otherwise be present in theoutput of a motion or orientation sensing device due to these stresses.As described above, temperature can be measured by two or more sensorsat various locations: one sensor may be on the motion or orientationsensing device, another adjacent the device on the isolation platformanother spaced from the device but within the package, and another onthe package itself. Other locations are contemplated. The data receivedby the temperature sensors is processed by the PID controller andcompensation software in the microcontroller. The PID controller in themicrocontroller can output a signal to the heat source circuit to outputa current to the heat source within the package to attempt to maintain adesired temperature of the device. The output data of the devicereceived by the microcontroller can then be compensated using the datafrom the temperature sensors and the ambient temperature from theambient temperature sensor.

The compensation software programmed into the microcontroller cancompensate the output data of the motion or orientation sensing deviceaccording to the following exemplary relationship:S _(comp) =S−(a ₁ T _(amb) +a ₂ T _(device) +a ₃)where S_(comp) is the data after being compensated (i.e., compensatedoutput), S is the detected movement or orientation prior tocompensation, T_(amb) is the ambient temperature, T_(device) is thedevice temperature, and a₁, a₂ and a₃ are compensation coefficients.While the relationship above is a first-order compensation equation, itshould be understood that second-order or higher-order compensationrelationships are contemplated and the above relationship is merelyexemplary.

The microcontroller can thus compensate the outputs of the motion ororientation sensing device based on ambient temperature as well as thedevice temperature (or inside package temperature). Multiple embodimentsof controls for the microprocessor are presented below that can beutilized to compensate the output of the device. The amount ofcompensation can be based on the temperature of the ambient and thedevice temperature. The combination of these temperatures can indicate atemperature distribution within the micro-package; having compensationfactors calculated based on these temperatures can increase the accuracyof the output of the device especially when the difference intemperature between the device (or inside package) and the ambient islarge.

As indicated by the teachings above, there is a correlation between theamount of power necessary for consumption by the heat sources, and theambient temperature compared with the internal temperature. For example,if the ambient temperature is low (e.g., −30° C.) but the desired devicetemperature is relatively high (e.g., 20° C.), the PID controller willcommand necessary power to be sent to and consumed by the heat sourcecircuitry. The amount of power consumed by the heat source circuitrydirectly corresponds with the amount of heating required to achieve ormaintain the desired internal temperature within the package. Therefore,since the controller knows the internal temperature from the internaltemperature sensors, and the controller knows how much power is beingconsumed by the heat source, the controller can infer the ambienttemperature causing such magnitude of consumption of power. This methodprovides a system that does not require an ambient temperature sensor,but can infer the ambient temperature based on the power consumption ofthe heat source. Therefore, in one or more embodiments of thisdisclosure, the ambient temperature is inferred and there is no ambienttemperature sensor coupled to the controller.

FIG. 4 illustrates an exemplary algorithm programmed into and actionableby the processor. This algorithm is one example for receivingtemperature and output data from a motion or orientation sensing device,controlling the oven or heat source within the package of the device,and compensating the output data based on the temperatures. Thecombination of temperature control and output data compensation providesan improved, more accurate motion or orientation sensing system.

At 100, the controller receives data representing the temperature of thedevice and the temperature around the device within the package from themultiple temperature sensors throughout the package, as explained above.The controller also receives data representing the ambient temperaturefrom an ambient temperature sensor.

At 104, the controller determines whether the motion or orientationsensing system is set to operate at a single set point (SSP) controlsetting. As will be explained below, a SSP control setting is a settingin which one single desired temperature is set and the controllercontrols the beat source inside the package to maintain that singledesired temperature. If the SSP control setting is active, then at 106the controller sets a constant desired temperature for the device andcontrols the beat source accordingly.

If, however, the system is not operating in the SSP control setting, thecontroller determines whether (or infers that) the system is operatingin a multiple set point (MSP) or continuous set point (CSP) controlsetting. As will be described in more detail below, in a MSP controlsetting the controller is programmed to set multiple (but not infinite)“stepped” temperatures for the device based on the ambient temperature;in a CSP control setting, the controller is programmed to set acontinuous desired temperature for the device that mimics the continuousnature of ambient temperatures. At 110, the controller acts accordinglyby controlling the heat source to change its output to achieve thedesired temperature in the device package that varies as the ambienttemperature varies.

At 112, the controller proceeds to receive output data representingmotion or orientation from the device itself. This output datarepresents the measured motion or orientation of the device as well asthe object the package is attached to.

At 114, the controller compensates the measured output data based ontemperature. In one embodiment, the data is compensated based on theformula explained above. In another embodiment, the data is compensatedbased on a look-up table of compensation factors that are set by thefactory based on the calibration result.

The controller then outputs the compensated output data at 116. Thiscompensated data can be output to a display, for example, or to othersystems that use motion or orientation data as an input. These othersystems are ones that require high-performance inertial sensors, suchas, for example, vehicular safety systems, robots, unmanned vehicles,helicopters, satellites, survey instruments, vibration monitoring,military weaponry (such as missiles), and other systems.

FIG. 5-8 represent graphical illustrations of the output of one or moremotion or orientation sensing devices prior to and after compensation.

First, FIG. 5A-5C illustrates exemplary graphical illustrations ofeffects of temperature on a sensor, and the resulting compensated outputbased on the temperature of the sensor. There is no oven in the package,such as the ovens described above, or, if there is an oven, the oven isnot controllable or variable to a set temperature. FIG. 5A illustratesthe relationship of the temperature of the device within the package tothe ambient temperature. As the ambient temperature increase, so doesthe device temperature due to no working heat source or oven within thepackage of the device.

FIG. 5B illustrates one example of creating calibration points that canbe used to compensate the output from the motion or orientation sensingdevice based on the ambient temperature (which indicates the devicetemperature). In this example, as the temperature decreases, the outputincreases in positive value, and as the temperature increases, theoutput decreases and falls below zero. There is no motion/orientationinput to the system, as indicated by the Y-axis. A certain number ofcalibration points are created during the calibration procedure. Thecalibration points can then be used in the compensation functionexplained above by the controller to compensate the output by thedevice. In another embodiment, the calibration points can be stored inmemory (e.g., a look-up table) coupled to the processor to compensatethe output data by the device. Missing points between the calibrationpoints can be interpolated.

The result of the compensated output of the device is shown in FIG. 5C.The goal of compensating the data is to reduce the temperature-inducederror of the device. Using calibration points does not reduce the errorto zero for all temperatures, as there are not an infinite number ofcalibration points available for the compensation function or thelook-up table.

FIGS. 6-8 are improvements upon the system and results exemplified inFIG. 5. In particular, the controlled temperature inside the packageimpacts the calibration points. Based on ambient temperature, the heatsource is activated to output a certain heat, and simultaneously thedata is compensated according to a compensation factor based on thetemperature inside the package and/or ambient temperature. A combinationof oven control and compensation functions reduces errors and improvesaccuracy of the data output from the device.

FIG. 6A illustrates the results from a single set point (SSP) ovencontrol implemented by the microprocessor when controlling the heatsource inside the package. In a SSP oven control, the PID controlmaintains the temperature inside the package at a single temperature.The controller does so by constantly measuring the temperature insidethe package, and controlling and varying the current output by the heatsource circuit accordingly to maintain the temperature.

The plot of FIG. 5A is shown again in FIG. 6A for comparison tohighlight the difference between a SSP oven control and a case in whichno oven control is provided.

FIG. 6B shows the calibration points that are created as describedabove. Because the temperature within the package is maintained at asingle set point, the controller can assume the difference betweenambient temperature and the single set point varies correspondingly withthe ambient temperature. The calibration points can be used tocompensate the output data from the device based on the ambienttemperature alone. In another embodiment, the actual difference betweenthe actual temperature within the package and the ambient temperature isused to compensate the output data from the device. Missing pointsbetween the calibration points can be interpolated.

The calibration points can be used in the compensation functionexplained above by the controller to compensate the output by thedevice. Like before, in another embodiment, the calibration points canbe stored in memory (e.g., a look-up table) coupled to the processor tocompensate the output by the device.

The results of using the calibration points to compensate the outputfrom the motion or orientation sensing device is shown in FIG. 6C.Again, the compensation attempts to reduce the error in the output ofthe device. As shown in FIG. 6D, there remains inherent minute errors inthe calibrated results, as there are not an infinite number ofcalibration points available for the compensation function or thelook-up table. However, the error is reduced by using a combination ofboth the SSP oven control as well as the temperature compensationbecause the amount of output change is reduced due to SSP oven control.

FIGS. 7A-7D are similar to FIGS. 6A-6D, except that the results of thecontrol scheme illustrated in FIGS. 7A-7D are the results of a multipleset point (MSP) oven control rather than a SSP oven control. In a MSPoven control system, the microcontroller changes the oven settemperature as the ambient temperature changes so that the differencebetween the motion or orientation sensing device and the ambient remainswithin a certain range. This can save power in heating the device duringtimes of cold ambient temperatures because less heat output is requiredbecause the temperature difference between the oven set point (thus thedevice temperature) and the ambient temperature is smaller (compared tothe SSP case). As shown in FIG. 7A-7B, the device temperature can be setsuch that multiple ambient temperatures correspond to a singleoven-controlled device temperature. This can be referred to a “stepped”increase in device temperature, as the device temperature increases insteps as the ambient temperature increases linearly. The resultingcalibration points of FIG. 7B may correspondingly decrease in a slightlyimbalanced “stepped” fashion with slight slope along each “step.”

The results of the calibrated output from the device (shown in FIG. 7D)provide similar results as those of FIG. 6D except for the chance ofreduced accuracy in transition regions between oven set points. However,an increased accuracy can be provided between the transition points, andless power can be used in heating the device, especially in coldertemperatures (compared to the SSP case). Missing points between thecalibration points can be interpolated.

FIGS. 8A-8C are similar to FIGS. 6A-6C and 7A-7C, except that theresults of the control scheme illustrated in FIGS. 8A-8C are a result ofa continuous set point (CSP) oven control. In a CSP oven control, themicrocontroller is programmed to alter the oven set temperaturecontinuously as the ambient temperature changes to maintain a constanttemperature difference between the device and the ambient temperature.This allows the oven to be operated with a relatively low amount ofpower input (compared to the SSP case).

The output from the device changes continuously as the ambienttemperature changes. Similar to the case in which no oven control isprovided (FIG. 5B), the output decrease sharply as CSP oven settemperature (thus the device temperature) increases, and then decreasesat a reduced rate. As in the prior oven control systems, the data outputfrom the device can be corrected and calibrated based on the calibrationdata. Missing points between the calibration points can be interpolated.

The combination of a continuous set point (CSP) oven and temperaturecompensation can result in increased performance than calibration alonebecause the feedback oven control can eliminate a high frequencytemperature noise, for example.

The processes, methods, or algorithms disclosed herein can bedeliverable to/implemented by a processing device, controller, orcomputer, which can include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, or algorithms can be stored as data and instructions executableby a controller or computer in many forms including, but not limited to,information permanently stored on non-writable storage media such as ROMdevices and information alterably stored on writeable storage media suchas floppy disks, magnetic tapes, CDs, RAM devices, and other magneticand optical media. The processes, methods, or algorithms can also beimplemented in a software executable object. Alternatively, theprocesses, methods, or algorithms can be embodied in whole or in partusing suitable hardware components, such as Application SpecificIntegrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs),state machines, controllers or other hardware components or devices, ora combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging size, serviceability, weight,manufacturability, ease of assembly, etc. As such, to the extent anyembodiments are described as less desirable than other embodiments orprior art implementations with respect to one or more characteristics,these embodiments are not outside the scope of the disclosure and can bedesirable for particular applications.

What is claimed is:
 1. A system for improving accuracy in a motion ororientation sensing device, the system comprising: an isolation platformhaving a device mounting region and an isolation structure providingmechanical and electrical connections between the device and componentsnot located on the device-mounting region; a heat source disposed on theisolation platform; a device disposed on the isolation platform; and atleast one internal temperature sensor disposed in a local area on theisolation platform adjacent the device and configured to detect atemperature of the local area; at least one controller programmed to:receive internal temperature signals from the at least one internaltemperature sensor indicating the temperature of the local area, receivesignals indicating an ambient temperature of an ambient environment,control the heat source to achieve a desired temperature of the localarea, receive signals from the device, and compensate the receivedsignals from the device by a compensation factor that varies based on acombination of the temperature of the local area and the ambienttemperature.
 2. The system of claim 1, further comprising an ambienttemperature sensor disposed away from the isolation platform andconfigured to output signals indicating an ambient temperature of theambient environment.
 3. The system of claim 2, wherein the compensationfactor varies based on a comparison between the temperature of the localarea and the ambient temperature.
 4. The system of claim 2, wherein thecontroller is further programmed to compensate the received signal fromthe device according to the following relationship:S _(comp) =S−(a ₁ T _(amb) +a ₂ T _(devic) +a ₃) where S_(comp) iscompensated output, S is detected motion or orientation beforecompensation, T_(amb) is the temperature of the ambient environment,T_(device) is the temperature of the local area, and a₁, a₂ and a₃ arecompensation coefficients.
 5. The system of claim 1, wherein the signalsindicating the ambient temperature of the ambient environment aresignals from a heat source or an associated controller indicating amagnitude of power consumed by the heat source in achieving the desiredtemperature of the local area.
 6. The system of claim 5, wherein the atleast one controller is further programmed to estimate the ambienttemperature based on the magnitude of power consumed by the heat source.7. The system of claim 1, wherein the at least one controller is furtherprogrammed to control the heat source such that the desired temperatureof the local area achieves a plurality of set temperatures, each settemperature corresponding to a plurality of ambient temperatures.
 8. Thesystem of claim 7, wherein the set temperatures increase in a steppedfashion as the ambient temperature increases.
 9. The system of claim 7,wherein the set temperatures increase continuously as the ambienttemperature increases.
 10. The system of claim 1, wherein the at leastone internal temperature sensor includes a first temperature sensor anda second temperature sensor, wherein the at least one controller isfurther programmed to determine a gradient of temperature of the localarea based on received signals from the first and second temperaturesensors, and wherein the compensation factor varies based on thegradient of temperature.
 11. The system of claim 10, wherein the desiredtemperature of the local area is based on the gradient of temperature.12. The system of claim 1, wherein the at least one controller isfurther programmed to retrieve the compensation factor from a calibratedlookup table based on the temperature of the local area.
 13. The systemof claim 1, wherein the device is a single gyroscope, multiplegyroscopes, a single accelerometer, multiple accelerometers, a singlemagnetometer, or multiple magnetometers or a combination thereof. 14.The system of claim 1, wherein the heat source is a plurality of heatsources, each heat source disposed within the package and coupled to theat least one controller.
 15. The system of claim 1, wherein thetemperature sensor is integrated into the device.
 16. A computerizedmethod of compensating an output of a device, the method comprising:receiving a local temperature signal from a temperature sensorindicating a temperature of the local area of an isolation platform;sending a signal to a heater to heat the local area to a variablepredetermined temperature; receiving output signals from the devicedisposed on the isolation platform and in the local area; via a signalprocessor, compensating the output signals received from the device bycompensation factors that vary based on the local temperature; andoutputting, from the signal processor, compensated output signals basedon the compensating.
 17. The computerized method of claim 16, furthercomprising receiving an external-temperature signal indicating anambient temperature away from the isolation platform, wherein thecompensation factors vary based on a combination of the temperature ofthe local area and the ambient temperature.
 18. The method of claim 17,wherein the variable predetermined temperature increases in a steppedfashion as the ambient temperature increases linearly, such that thestep of heating includes heating the local area in a stepped fashion asthe ambient temperature increases linearly.
 19. The method of claim 17,wherein the variable predetermined temperature increases continuously asthe ambient temperature increases linearly, such that the step ofheating includes heating the local area in a continuously-increasingfashion as the ambient temperature increases linearly.
 20. The method ofclaim 16, wherein the heat source is a plurality of heat sources, eachheat source is disposed on the isolation platform and coupled to thesignal processor.